ACTIVATION OF AN INTERLEUKIN-1 CONVERTING ENZYME-DEPENDENT APOPTOSIS PATHWAY BY GRANZYME-B

Cytotoxic T lymphocytes (CTL) can induce apoptosis through a granzyme B-based killing mechanism, Here we show that in cells undergoing apopt osis by granzyme B, both p45 pro-interleukin 1 beta converting enzyme (ICE) and pro-CPP32 are processed, Using ICE deficient (ICE -/-) mice, embryonic fibroblasts exhibit high levels of resistance to apoptosis by granzyme B or granzyme 3, while B lymphoblasts are granzyme B-resis tant, thus identifying an ICE-dependent apoptotic pathway that is acti vated by CTL granzymes, In contrast, an alternative ICE-independent pa thway must also be activated as ICE -/- thymocytes remain susceptible to apoptosis by both granzymes. In ICE -/- B cells or HeLa cells trans fected with mutant inactive ICE or Ich-1S that exhibit resistance to g ranzyme B, CPP32 is processed to p17 and poly(ADP-ribose) polymerase i s cleaved indicating that this protease although activated was not ass ociated with an apoptotic nuclear phenotype, Using the peptide inhibit or Ac-DEVD-CHO, apoptosis as well as p45 ICE hydrolysis are suppressed in HeLa cells, suggesting that a CPP32-like protease is upstream of I CE, In contrast, p34(cdc2) kinase, which is required for granzyme B-in duced apoptosis, remains inactive in ICE -/- B cells indicating it is downstream of ICE. We conclude that granzyme B activates an ICE-depend ent cell death pathway in some cell types and requires a CPP32-like Ac -DEVD-CHO inhibitable protease acting upstream to initiate apoptosis.